1. Field of the Invention.
The present invention relates generally to the servicing of railroad ties, and in particular to a vehicle for and a method of applying preservative to existing wooden railroad ties in situ.
2. Description of the Prior Art.
Wood has traditionally been, and will probably continue to be, the predominant material for railroad track ties. Wood has several advantages over alternative tie materials, such as concrete. Wood is a renewable natural resource and is available in many parts of the world at reasonable cost. Another important advantage of wood is its natural resiliency, which enables wooden railroad ties to absorb the dynamic loads that are associated with railroad traffic. Wooden railroad ties tend to be lighter in weight than comparable concrete railroad ties, and therefore can be relatively easily handled by installation and maintenance crews and equipment.
A significant disadvantage to wood railroad ties, on the other hand, is that they can be susceptible to decay and deterioration. Since wood is a cellulose material, it is subject to damage from fungus, decay, termite infestation, and exposure to the elements in unprotected, outdoor environments.
Preservatives including coal tar creosote are commonly applied to structural wood members, such as railroad ties, that will be exposed to the elements. However, the protection provided by such preservatives tends to lessen over time because the preservatives are susceptible to the deteriorating effects of sunlight, precipitation, freeze-thaw cycles, etc. Thus, the useful service life of a railroad tie is generally limited by the effectiveness of its preservative treatment.
Railroad ties are particularly susceptible to damage and deterioration in the connection areas adjacent to each end where the tracks are attached. The normal construction of a railroad track involves the placement of ties at intervals of about eighteen to thirty inches in a roadbed of ballast comprising crushed rock or the like. A pair of steel plates are then placed on the connection areas of each tie to support the rails, and spikes are driven through the plates and into the railroad ties, the spike heads securing the rails in place by clamping the lower rail flanges to the plates.
The spikes penetrate interior portions of the ties that may have received little or no preservative. The tie ends are often split by the spikes, exposing other untreated interior portions. Under railroad traffic, these connection areas are naturally subjected to more stress than any other part of the railroad tie, whereby they tend to experience the greatest amount of wear. Moreover, the plates tend to collect and retain moisture, thereby exacerbating deterioration at the connection areas. On most wooden ties the condition of these connection areas tends to deteriorate more rapidly than other portions, yet the connection areas are the most critical for providing rail support and maintaining the integrity of the railroad. Hence, the useful service life of an entire railroad tie is generally limited by the structural integrity of its connection areas.
Several methods have heretofore been employed to correct railroad tie deterioration problems. For example, wood preservative can be injected into the tie connection areas, generally through the holes in the plates that are not occupied by spikes. In normal railroad construction two spikes per plate are used, although the plates typically have at least four holes. Thus, each such plate has two holes available for preservative injection. Although railroad tie life can be prolonged somewhat by this method, a substantial amount of damaged or decayed wood material often remains. The additional preservative may slow the deterioration process, but generally it will not significantly improve the condition of the tie. When enough ties become so deteriorated that a railroad track is deemed unusable, the ties must be replaced at great expense in time and labor.
An intermediate procedure is sometimes employed whereby the tracks are removed, the connection areas are planed down by a resurfacing vehicle, preservative is applied to the exposed wood at the connection areas, and the tracks are remounted. Railroad maintenance equipment is available for removing the spikes, setting the rails aside, scooping out the surrounding ballast and planing the connection areas of the existing ties. Heretofore the preservative has generally been applied manually. However, manual application of the preservative is not particularly desirable because of the inherent difficulties in accurately dispensing predetermined quantities of preservative with manual applicators, the limitations on the amount of preservative that a worker can carry and the hazards to the worker associated with handling the preservative. Creosote-based preservatives are generally toxic and can irritate the skin and eyes of a worker exposed to them. Respirators, face masks and other protective clothing must normally be worn when handling such preservatives.
The present invention addresses these problems associated with preservative application by providing a device and a method for applying the preservative automatically, efficiently and safely.